The following information is provided to assist the reader in understanding technologies disclosed below and the environment in which such technologies may typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding the technologies or the background thereof. The disclosure of all references cited herein are incorporated by reference.
Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.
OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.
One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.
One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)3, which has the following structure:

In this structure, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.
As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.
As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.
As used herein, “solution processible” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.
More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.
It is difficult for currently available thin film deposition or encapsulation technologies to cover large size particles on OLEDs and other systems. The general trend is that larger particles require thicker films to provide coverage, which results in longer process time and increased cost.
OLEDs and other electronic/microelectronic devices including water vapor sensitive cathodes and organic materials degrade upon storage. The degradation is evidenced by formation of dark spots, which may be caused by the ingress of water vapor and oxygen vertically through the bulk of the thin film encapsulation (TFE) or through surface protrusion defects (particles) embedded in the TFE, or by the ingress of water vapor and oxygen horizontally through the edge of the TFE. In most cases, the dominant degradation mechanism is ingression of water vapor and oxygen through surface protrusions or particles.
One of the most studied thin film encapsulation technologies is a multilayer approach described, for example, in U.S. Pat. No. 6,548,912. The multilayer barrier of that approach includes alternate layers of inorganic and polymer films. A pair of inorganic and polymer layers is called a dyad. The multilayer approach works on the principle of delaying the permeant molecules from reaching the device by forming long and tortuous diffusion paths. The multilayer approach to protrusion/particles encapsulation provides redundancy in the number of dyads. When the particle size is large, the required number of dyads can be very large as illustrated in FIG. 1.
A number of common thin film deposition techniques used, for example, with inorganic materials/films are known to be anisotropic, directional or directionally limited. It is thus very difficult for deposited inorganic films to cover shadowed region under a protrusion. With reference to FIG. 2, a protrusion 10 may be defined as an entity that has or creates a shadowed region 20. Shadowed region 20 may be defined with respect to a columnar source of light having substantially the same orientation as a directional deposition technique. In FIG. 1, light from such a columnar source of light is represented by arrows 30, radiating from above (in the orientation of FIG. 2) and orthogonal to a surface 40 upon which protrusion 10 is positioned. Shadowed region 20 corresponds to the volume under the perimeter of protrusion 10 and above surface 40. In FIG. 2, protrusion 10 is illustrated as a spherical particle, but protrusions can be of generally any shape (whether regular or irregular).
Referring again to FIG. 1, under the technique of U.S. Pat. No. 6,548,912, inorganic barrier layer 60a, 60b, 60c, and 60d are alternately deposited with polymer layer 70a, 70b 70c and 70d on a surface of a device/substrate 50 upon which a plurality of protrusion defects 10 (for example, particles) are present. Polymer layers 70a, 70b 70c and 70d fill the shadowed region 20. However, protrusion 10 is relatively large, and four dyads are required to fill shadowed region 20 in FIG. 2. A fifth inorganic layer 60e (illustrated in broken lines) will be able to provide continuous coverage along the surface around protrusion 10. Generally, the thin film layer stack must have at least half of the thickness of protrusion 10 to provide a good surface profile to support a continuous coating. Materials may be deposited on top of the protrusions (not shown in the figures).
Other approaches have been proposed to deposit thin film as, for example, encapsulation barriers for microelectronic devices. One example is atomic layer deposition (ALD). However, it is difficult to provide good coverage of protrusions with ALD. Also, when the protrusion can move (for example, in the case of particles), ALD has problems holding the protrusions in place.
U.S. Patent Application Publication No. 2008/0102223 discloses an encapsulation technique using a single layer barrier. Because the material is deposited in a plasma-enhanced chemical vapor deposition (PECVD) chamber, it is possible to achieve a good conformal coating to cover a protrusion. However, film thickness may need to be increased to adequately cover larger protrusion.
Increasing film thickness translates into longer deposition time, more material usage, and eventually higher cost. Furthermore, there is no guaranty that large protrusions can be fully covered even using thicker films.